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金属矿产资源采、选、冶炼过程产生的大量废弃尾矿无序堆放是矿区周边环境中重金属的重要来源,对当地居民健康及生态系统构成了潜在威胁[1-2]。贵州兴仁滥木厂汞铊矿是中国西南地区典型的多金属矿山,具有较长的开采历史[2]。虽然采矿活动已经停止了300多年,但遗留下大量的废渣被无序堆放在矿区周边土壤上,这些裸露废渣暴露于自然环境中长期遭受风蚀和水蚀作用,废渣中重金属持续释放、迁移至周边水土环境中,对矿区周边环境造成严重污染[3-5]。植被恢复是减少尾矿堆场遭受水蚀和风蚀的有效策略[4],其中,建立先锋草本植物是恢复尾矿堆场生物地球化学功能的关键环节[5],这是由于先锋草本植物能耐受尾矿中高浓度重金属,有利于尾矿生境条件改善及其它修复植物引进[6]。三叶草(Trifolium repens)是广泛用于改善尾矿堆场环境条件的先锋草本植物[7]。随着尾矿堆场植被演替,先锋草本植物将被其他优势植物所取代,先锋草本凋落物分解可产生大量的溶解性有机质(dissolved organic matter,DOM)[8]。有研究[9-10]表明,DOM是一种活性极强的有机成分,其对植物生长、微生物代谢和重金属迁移转化过程具有重要影响。DOM含有丰富的活性有机官能团(如酚羟基、羧基、羰基等),其通过与土壤重金属发生一系列反应(如离子交换吸附,氧化还原,络合和甲基化),进而影响土壤中重金属的迁移转化过程[11-12]。然而,关于尾矿堆场生态修复过程中先锋草本植物凋落物源DOM对尾矿中重金属迁移转化影响的研究鲜有报道。
贵州兴仁滥木厂汞铊矿历史活动遗留下的废渣成分较复杂,其含有多种对DOM敏感的特征重金属,包括铊(Tl)、汞(Hg)、砷(As)和锑(Sb)等。然而,在废渣堆场生态修复过程中,先锋草本植物凋落物源DOM对废渣特征重金属迁移转化的影响仍尚不明晰。基于此,本研究拟以典型汞铊矿废渣以及三叶草凋落物源DOM为研究对象,通过开展批次培养实验,探究三叶草凋落物源DOM对废渣中特征重金属释放行为的影响,明晰废渣-DOM体系中重金属释放特征的驱动因子,旨在深入理解废渣堆场生态修复过程中先锋草本植物凋落物源DOM对废渣中重金属地球化学行为的影响,以期为开展生态修复的废渣堆场的科学管理提供理论依据。
先锋草本植物凋落物源溶解性有机质对典型汞铊矿废渣中重金属释放特征的影响
Effects of dissolved organic matter from pioneer herb plant on the release characteristics of heavy metals in a typical mercury-thallium mining waste slag
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摘要: 先锋草本植物广泛应用于尾矿堆场生态恢复,其凋落物分解是尾矿中溶解性有机质(DOM)的重要来源。然而,先锋草本植物凋落物源DOM对尾矿中重金属释放特征的影响尚不清晰。本研究以典型汞铊矿废渣及三叶草凋落物为研究对象,通过开展批次培养实验探讨了三叶草凋落物源DOM对废渣中重金属(Hg、As、Sb、Tl)释放特征的影响。结果表明,三叶草凋落物源DOM的成分主要为类络氨酸类物质、陆生类腐殖质物质和微生物类腐殖质物质。DOM的添加明显促进废渣中Hg和As的释放,抑制Tl和Sb的释放,浸出液中重金属的浓度依次为As>Tl>Hg>Sb。DOM的添加有利于废渣中Hg(Ⅱ)的溶出,促进废渣中As(Ⅴ)还原为As(Ⅲ)。主成分和相关性分析结果表明,DOM的自身组分及其对环境条件(pH、Eh)的改变是影响废渣重金属释放特征的主要因素。以上研究结果可为深入认识开展生态修复的废渣堆场上重金属的地球化学过程及环境风险提供参考。Abstract: Pioneer herbs are widely used for the ecological restoration of mine tailing sites, and their litter decomposition is an important source of dissolved organic matter (DOM) in the mine tailings. However, the effect of DOM derived from pioneer herb litter on the migration and transformation of heavy metals in the mine tailings remains unclear. In this study, the typical mercury-thallium mining waste slag and litter of Trifolium repens were used as research objects. The batch culture experiments were conducted to investigate the effects of DOM derived from the litter of Trifolium repens on the release characteristics of heavy metals (Hg, As, Sb, and Tl) in the waste slag. The results showed that the main components of DOM were tyrosinoid-like substances, terrestrial humus-like substances, and microbial humus-like substances. DOM addition significantly promoted the release of Hg and As, but inhibited the release of Tl and Sb in the waste slag, and the heavy metal concentrations in the leachate exhibited the following order: As>Tl>Hg>Sb. DOM addition facilitated the release of Hg(Ⅱ) and the reduction of As(Ⅴ) to As(Ⅲ) in the waste slag. Principal component and correlation analysis indicated that DOM components and the corresponding changes in environmental conditions (e.g., pH and Eh) were the main factors affecting the release characteristics of heavy metals in the waste slag. The results can provide a theoretical basis for understanding the geochemical processes and environmental risks of heavy metals in the waste slag sites undergoing the ecological restoration.
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